The conventional technology is described below for a wiring material for LSI as an example of current-driven conductive material. As wiring material for LSI, at present, such materials as Al, Al--Si alloy prepared by mixing several percents of Si in Al or Al--Si--Cu alloy in which a small quantity of Cu is mixed have been used.
As a degree of integration in LSI becomes higher and higher, a width of wiring therein becomes thinner and thinner with the length becoming increasingly longer, and also a number of wires used therein is becoming larger. On the other hand, in LSI, a higher operating speed is required together with a higher degree of integration, and as a result, a current flowing in a wire has been becoming increasingly larger. Namely density of a current flowing per unit cross section has been becoming higher and higher as a degree of integration becomes increasingly higher. However, when a large current flows in a metallic wire, metal atoms moves in a direction reverse to that in which the current flows, and as a result a portion of the wire may become thinner and thinner and sometimes result in breaking of wire. This phenomenon is called electro-migration. Furthermore when density of a current flowing through wiring increases, heat stress due to Joule heat generation in the wiring and the wiring is deteriorated. This phenomenon is called stress migration. It is not too much saying that reliability of metal wiring is decided by the two phenomena described above. For this reason, in order to develop a high performance LSI, a material having a high capability to withstand the electro-migration and stress migration is required, and in development of the material, it is important to strictly evaluate the material's capability to withstand the phenomena. The conventional method of evaluating reliability of wiring is as described below.
In the conventional type of LSI wiring, only a current having a density of around 105 A/cm.sup.2 is flown, but in the reliability test, a current with a current density of 10.sup.6 A/cm.sup.2, 10 times or more larger than the usual one, is flown to shorten the time required for a wiring reliability test. In addition, to furthermore promote deterioration, a method is employed in which a temperature of atmosphere is raised to around 250.degree. C. However, also in the deterioration promoting test as described above, breaking of wiring does not occur within a month in case of ordinary Al--Si alloy wiring having a short life, and actually, for instance, resistance of wiring is monitorred, and a time required until the resistance increases by 5% or by 10% is used as a life of the wiring. In spite of that, in many cases, a period of time ranging from several weeks up to around one month is required until a resistance value of wiring shows the change as described above, and in case of material for wiring having a higher reliability, which is a target for material development, a further longer time is required, and for the reasons as described above, practically the method is not effective as a method of evaluating material for wiring.
So, in order to furthermore shorten a time required for a deteriorating test, it is desired to flow a current having a higher density. However, if it is tried to flow a current with a high density, the wiring is heated because of Joule's heat, and consequently the resistance becomes higher, which furthermore promote heating of the wiring, and as a result the wiring temperature becomes uncontrollable, which results in melting of the wiring.
To solve this problem, the present inventor succeeded in shortening a time required for a reliability test for wiring, without causing melting of wiring, by repeating the operational sequence comprising the steps of flowing a first current in a wiring pattern, then measuring a resistance value of the wiring, then flowing a second current having a larger current value than the first current to heat this wiring, simultaneously controlling temperature of the wiring pattern by means of cooling it from the outside to prevent the wiring temperature from becoming uncontrollable, turning off the second current, and then again flowing the first current (Japanese Patent Application No.126732/1991). However, although it is possible to shorten a time required for a reliability test of wiring, a problem was found that whether the wiring is deteriorated due to electro-migration or due to stress migration can not be discriminated. To furthermore minutely investigate a reliability of wiring, it is required to discriminate which of these phenomena is the case for deterioration o wiring.
The present invention was made in the light of the circumstances as described above, and it is an object of the present invention to provide a method of evaluating current-driven conductive material which enables independent evaluation of a capability of wiring material to withstand electro-migration and stress migration within a short period of time and also enables feedback of test data effective for development of wiring material.